FIG. 12 shows in section, by way of example, a semiconductor production apparatus disclosed in Japanese Published Patent Application 61-279120. The apparatus has a reaction vessel 1 and a susceptor 3 which is rotatably disposed in a lower portion of the reaction vessel 1 for supporting a substrate 2, such as a silicon substrate. A light-transmitting glass window 4 is disposed in an upper wall of the reaction vessel 1 opposite the susceptor 3. A cover plate 5 is disposed around the light-transmitting glass window 4. A lamp housing 7 is disposed outside the light-transmitting glass window 4. A light source 6, such as an infrared lamp, is disposed inside the lamp housing 7 opposite the susceptor 3. A reaction gas mixture, e.g., a gas mixture containing silane, is introduced into the reaction vessel 1 through a reaction gas supply port 8. A carrier gas which does not contain any reaction gas is introduced into the reaction vessel 1 through a carrier gas supply port 9. The gas inside the reaction vessel 1 is discharged from a gas discharge port 10.
A substrate 2 is placed on the susceptor 3 and a rotary driving means (not shown) is activated to rotate the susceptor 3. The infrared lamp 6 irradiates the substrate 2 through the light-transmitting glass window 4, thereby heating the substrate 2. A reaction gas mixture is introduced into the reaction vessel through the reaction gas supply port 8 and the reaction gas flows parallel to the substrate 2 in the region near the substrate. At the same time, a carrier gas in introduced into the reaction vessel 1 through the carrier gas supply port and the carrier gas flows parallel to the substrate 2 in the region near the light-transmitting window 4.
The reaction gas mixture containing silane is thermally decomposed by the heat from the substrate 2 so that film precursor radicals are formed. The film precursor radicals reach the surface of the substrate 2 so that a silicon polycrystalline film is formed on the surface of the substrate 2. The surplus reaction gas and the carrier gas are discharged from the reaction vessel 1 through a discharge port 10.
In this known apparatus, the film precursor radicals are prevented from diffusing to the region near the light-transmitting glass window 4 because the carrier gas flows in the region near the light-transmitting glass window 4 so that deposition of the film precursor radicals on the light-transmitting glass window 4 is avoided. Therefore, prevention of diffusion of the radicals toward the light-transmitting glass window 4 at the downstream side is less effective than at the upstream side of the flow of the reaction and carrier gases. Consequently, deposition of the film precursor radicals on the light-transmitting glass window 4 cannot be perfectly avoided at the downstream side, particularly when the substrate 2 is large.
The deposition of the film precursor radicals on the light-transmitting glass window 4 undesirably impairs the light-transmitting characteristics of the glass window 4 and heating of the substrate 2, making it difficult to develop a uniform temperature distribution across the substrate, a critical parameter controlling the rate of formation of the film on the substrate 2. Furthermore, unnecessary reaction products tend to be trapped in the film at the surface of the substrate and impair the quality of the film.
In recent years, a so-called lamp heating method has been proposed in which a substrate can be heated in a short time by means of a lamp during production of a semiconductor film. A semiconductor film production apparatus employing the lamp heating method is disclosed in Mat. Res. Soc. Symp., Volume 46, page 57. FIG. 13 is a schematic sectional view of this apparatus. For the purpose of forming, for example, a thin silicon film on a silicon substrate 2, silane gas is introduced into a reaction vessel 1 through a gas supply port 8. In order to hermetically seal the gap between the reaction vessel 1 and the light-transmitting glass window 4, an "0" ring is interposed therebetween. The substrate 2 is heated with light transmitted from an infrared lamp 6 to the substrate through a light-transmitting window. The surface of the substrate 2 is heated to a high temperature as a result of absorption of the infrared light so that the silane gas is decomposed on the surface of the substrate 2, whereby a thin film of silicon is formed. After reaction, the gas is discharged from the reaction vessel through a gas discharge port 10.
In this known semiconductor production apparatus, part of the infrared light from the infrared lamp 6 passes through the light-transmitting glass window 4 and is absorbed by the "O" ring 11. Therefore, the temperature of the "O" ring 11 is raised to a level above its rated temperature so that the "O" ring is degraded and the reaction vessel seal fails. Consequently, problems are encountered, such as an inability to produce high-quality films due to mixing of air with the high-purity reaction gases and dangerous leakage of the reaction gas from the vessel 1 into the atmosphere.
FIG. 14 shows a known thin film forming apparatus, particularly an apparatus for forming a thin film in a CVD process, which is disclosed in the Photo-Thin-Film Technology Manual, published by Optronics Kabushiki Kaisha. In this apparatus, the substrate 2 is heated to a suitable temperature and, at the same time, SiH.sub.4 carried by N.sub.2 is introduced together with O.sub.2 through a nozzle of a reaction gas supply portion 13 onto the substrate 2 and extracted from a discharging portion 14 whereby a silicon oxide film is formed on the substrate 2 through a chemical reaction. Difficulties in controlling the flow of the reaction gas, which adversely affects the uniformity of the film thickness of the deposited film, have been encountered with this apparatus.